The invention described herein relates generally to x-ray lasers and more particularly to resonantly photo-pumped x-ray lasers.
The first operational laboratory x-ray laser, which used collisional excitation as the pumping mechanism, was taught by Campbell and Rosen in U.S. Pat. No. 4,827,479 issued May 2, 1989. Moreover, this x-ray laser is also described by Rosen et al. in Physical Review Letters 54, 106 (1985), with a discussion of the experimental demonstration of the laser provided by Matthews et al in Physical Review Letters 54, 110 (1985). This seminal work was also reported in Physics Today, March 1985, at pages 17 to 19. Additionally, a recent review of soft x-ray lasers is provided by Matthews and Rosen in Scientific American, December 1988, at pages 86 to 91.
The following are representative of the state-of-the-art in x-ray laser research and speculation: Cochran et al, in U.S. Pat. No. 4,803,687 issued Feb. 7, 1989, describe a sodium-neon laser target wherein Ne IX (He-like Ne) is resonantly photo-pumped by Na X (He-like Na). A carbon thermal buffer layer is required between the sodium and neon layers.
Hagelstein, in U.S. Pat. No. 4,660,203 issued Apr. 21, 1987, describes x-ray lasers wherein various multiply ionized species are used to pump high energy transitions in helium-like or hydrogen-like N, O, F, C or rare gases. For example, F-like Ti is indicated as a pump material at 24.907A to drive a He-like N laser. The lasant material is located within a hollow container fabricated from parylene, or a material substantially transparent to radiation in the wavelength range from 60 to 300 Angstroms, and is multiply-ionized and undergoes at least one super-radiant laser transition.
Silfvast, in U.S. Pat. No. 4,592,064 issued May 27, 1986, discloses a scheme that permits high gain at visible and UV wavelengths in species such as Cd and Zn. A population inversion is established by producing a plasma that generates x-ray pulses in the 150 to 650 Angstrom (.ANG.) wavelength range.
Elton, in U.S. Pat. No. 4,592,056 issued May 27, 1986, describes x-ray lasing systems wherein a neon-like sulfur plasma is used to pump a lithium-like neon plasma, and wherein a lithium-like silicon plasma is used to pump a lithium-like magnesium plasma.
Harris, in U.S. Pat. No. 4,380,072 issued Apr. 12, 1983, describes a method of exciting atoms to a storage level, then irradiating the excited atoms and thereby raising them to a higher level, whereupon the atoms lase to a lower level, other than ground, which is simultaneously emptied. This method results in the generation of XUV radiation.
Mani et al, in U.S. Pat. No. 4,229,708 issued Oct. 21, 1980, describe an x-ray laser wherein lithium-like atoms or ions are stimulated to lase by resonant or non-resonant antistokes Raman processes. The laser functions by directing filtered, black-body radiation in the soft x-ray region into a lithium-like vapor.
Jaegle et al, in U.S. Pat. No. 3,826,996 issued Jul. 30, 1974, describe obtaining a medium having a negative absorption coefficient within the ultra-violet and x-ray range, by focusing a giant-pulse laser beam on an aluminum target.
Despite tremendous progress in the development of x-ray lasers over the last several years, only two pumping mechanisms have been used to create gain and produce laser output. These have been collisional excitation, in the case of Ne-like and Ni-like lasers, and recombination, in the case of H-like and Li-like lasers.
Proposals have been made of many schemes using the resonant photo-pumping mechanism to drive various x-ray lasers; however, the resonant photo-pumping mechanism has not as yet been actually demonstrated in the x-ray, or even the soft x-ray, region. The shortest wavelength at which significant gain has been measured using resonant photo-pumping is 2163 .ANG. in beryllium-like carbon pumped by a manganese plasma, in work reported by Qi and Krishnan, Phys. Rev. Lett. 59, 2051 (1987).
Nilsen, in U.S. Pat. No. 4,977,572 issued Dec. 11, 1990, describes a resonantly photo-pumped x-ray laser that enhances the gain of several laser lines that also lase because of collisional excitations and recombination processes. An aluminum and erbium foil combination is driven by two beams of intense line focused optical laser radiation. Ground state Ni-like Er ions are resonantly photo-pumped by line emission from H-like Al ions to produce 54-90 .ANG. radiation.
Nilsen in U.S. patent application Ser. No. 07/420,433, filed Oct. 12, 1989, describes a resonantly photo-pumped x-ray laser in the 23-44 Angstrom range. A silicon and dysprosium foil combination is driven by two beams of intense line focused optical radiation. Ground state nickel-like dysprosium ions are resonantly photo-pumped by line emission from hydrogen-like silicon ions.